The big issue on the OP's subject car is whether the bearings are OK or if they are too damaged. That's the risk and unknown. The fact it overheated means a lot of coolant was lost inside the engine. That's a bad sign indicating potential for bearing damage. Sad that a vehicle with otherwise many good miles left on it may end up costing too much to repair vs value. I agree that the OP should only take on the job if he owns the vehicle, too much risk for the customer who seems to be tight financially already.
I have this potential water pump problem on 2 vehicles: 2008 Edge 3.5 (180K) and 2016 Explorer 3.5 (29K). My hopeful plan is to just keep up on regular coolant changes, and of course regular oil changes. Since both of these affect the seals which seems to be the failure area, then once the seal leaks, it takes out the water pump bearing. Obviously not a foolproof method, but it's really all one can do beyond the easy watching the coolant reservoir level, the weep hole on the block and oil condition/color when doing oil changes. If the water pump replacement job wasn't such a big PITA job it would be candidate for preventative replacement.